1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device and an oscillation frequency calibration method.
2. Description of the Related Art
Oscillators are widely used in semiconductor integrated circuits. Before the oscillators are shipped, it is necessary to calibrate an error in an oscillator frequency that occurs in a manufacturing process. Conventionally, a method of calibrating an oscillation frequency is known. In recent years, oscillators having a tight tolerance in oscillation frequency with respect to a temperature change are often required. There is a demand for a solution that satisfies such a need.
As an example of the solution, means for measuring a correspondence relation of an oscillation frequency with respect to an absolute temperature and determining a calibration value is known. However, in this calibration work, extremely long converging time is required when temperature is accurately changed (e.g., changed from T1 to T2). Therefore, the calibration work is a cause of an increase in cost for the calibration. In some case, unless the calibration is applied to the temperature in an entire temperature compensation range, the performance of an oscillator at the time of shipment cannot be guaranteed and a further increase in calibration cost is caused. Therefore, there is a demand for a method that can end the calibration work for an oscillation frequency in a short time.
The related art represented by Japanese Patent Application Laid-Open No. 2008-311884 discloses an oscillation frequency control method that can adjust, when temperature changes, an oscillation frequency to a predetermined reference frequency with high responsiveness and keep the oscillation frequency constant.
However, the related art represented by Japanese Patent Application Laid-Open No. 2008-311884 relates to control of an oscillation frequency with respect to a temperature change after the shipment of an oscillator and cannot satisfy the need for reducing time required for the calibration work for the oscillation frequency.
It is an object of the present invention to provide a semiconductor integrated circuit device and the oscillation frequency calibration method that can reduce the time required for the calibration work for the oscillation frequency of the oscillator.